Intaglio inks and water-wipe intaglio printing processes are well-known in the art.
Typically, intaglio printing refers to a printing method using a plate that contains engraved areas which transfers the contained ink to the surface of a substrate, thereby forming the printed image. The plates may be engraved by machine, by hand or by a chemical etching process. The intaglio process may be either a sheet-fed or a web-fed process.
Security documents are mostly printed with an intaglio process using curved intaglio plates on sheet-fed presses. Security documents include banknotes, stamps, certificates, fine-line documents and similar printed substrates. The images are primarily line images and the inks used are of a high-viscosity type. Nowadays, water-wipe intaglio and paper-wipe intaglio processes are the two most widely used printing methods. For a water-wipe intaglio printing process, an engraved plate is inked by an inking roller system which presses ink into the engravings. The excessive ink surrounding the various engravings is then wiped by a wiping roller system which comprises a clean vinyl or rubber roller. The wiping roller contacts the engraved plate and wipes the excessive ink away from the non-image areas in a continuous manner. Prior to re-contacting the intaglio plate, the wiping roller is brushed with a water-wipe solution to emulsify the ink for the removal of the ink. The inked and wiped plate is brought into contact with a substrate. Under high pressure, the printing is thus done with the transferring of ink from engraved plate to the substrate. The printed substrates are removed from the press and dried. The printing process is then repeated. The wiping solution may contain an organic solvent (e.g., trichloroethylene) which is usually not used for hazardous reasons. The water-wipe solution may contain up to 1% by weight sodium hydroxide and up to 1% by weight sulfonated castor oil and/or surfactant (e.g., Teepol).
During this printing process, 80% to 90% of the water-wipe intaglio ink carried to the plate cylinder is wasted and wiped to the wiping solution. Only 10% to 20% of the ink forms the printed image. Thus, it is necessary to separate the wasted intaglio ink from the wiping solution which is an expensive process. For the wiping solution that contains organic solvent, this separation can be done by distillation. Usually, the treatment for the water-wipe solution is to add to the solution some iron chloride, or diatomaceous earth, etc. Processes of filtration and neutralization of the aqueous phase are then followed. The wasted intaglio ink is treated as solid waste and is not reused. This kind of waste must be incinerated, which is expensive and generates hazardous solids and fumes.
The object of this invention is to reduce the hazardous waste and to enhance the efficiency of intaglio ink consumption with the aid of recycling and refurbishment of the wasted intaglio ink from the water-wipe solution.
Other processes invented to try to reduce the consumption of intaglio inks are disclosed in French Patent Number 1,564,653, referring to the principle of wet offset balance between water and ink on the plate, and Swiss Patent Number 628,289, suggesting the installation of an anti-adherence layer to counter inkings on the non-image areas on the plate and U.S. Pat. No. 4,391,638 proposes a method for reclaiming waste offset ink for disposal purposes. Some printers try to collect ink by using a pre-wiping cylinder, but the collected ink has often been polymerized, leading to a degraded ink quality. None of these processes conserve the consumption of intaglio ink by recycling the wasted intaglio ink extracted from the water-wipe solution.
Conventional intaglio inks used in the art are dried or cured by oxidation. This type of ink contains oleoresinous or alkyd resin-type associated with driers. The oleoresinous may be a linseed oil or solid resin such as phenolic resin or maleic resin soluble in a mineral oil (boiling point: 160.degree. C. to 330.degree. C.) or unsaturated oil or in a polyol. The ink contains some fillers such as calcium carbonate or barium sulfate associated with inorganic or organic pigments. Another type of intaglio inks are Electron Beam (EB) inks cured by radiation mechanism. The EB intaglio inks contain acrylic polymers or oligomers or monomers as varnishes. The intaglio inks must be able to be wiped from the wiping cylinder in a water solution containing up to 1% by weight caustic soda and up to 1% by weight sulfonated castor oil. This water-wipe solution is, in fact, alkaline. However, it is possible that in some instances an acid water-wipe solution may be employed.
Usually, the water-wipe solution containing the wasted intaglio ink cannot be directly filtrated because of the viscosity of the waste. Thus, to stabilize the flocculation, the solution is treated by adding some iron chloride or diatomaceous earth so that the wasted intaglio ink can be removed by filtration. However, this destroys the ink so that it cannot be reused. Thus, there is a long-felt need in the art for separating the ink from the water-wipe solution so that the ink is not destroyed and so that the ink can be reused or recycled.